


Quite the Mishap

by Spingtail



Series: Mishap AU [1]
Category: Undertale (Video Game)
Genre: Body Horror, Insomnia, i wrote this instead of eating dinner i hope you're happy, in a way anyway, mishap au
Language: English
Status: In-Progress
Published: 2020-02-01
Updated: 2020-08-19
Packaged: 2021-02-28 03:13:36
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 4
Words: 3,208
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/22516813
Author URL: https://archiveofourown.org/users/Spingtail/pseuds/Spingtail
Summary: Sans can't sleep, so he goes to check up on his brother.
Series: Mishap AU [1]
Series URL: https://archiveofourown.org/series/1621690
Comments: 29
Kudos: 124





	1. A Metallic-Scented Red Stain

Sans couldn’t sleep.

He didn’t know what had woken him up, but when he had felt like everything in the world had suddenly gone wrong all at once, he figured he could just sleep it off.

That was four hours ago. 

He let out a loud huff, holding his pillow over his face when light began to leak in through his window. He regretted not bothering to get any curtains.

As happy as he usually was to lay down and do nothing, it tended to be better when it wasn’t so damn  _ boring. _

Finally giving in, he lifted the pillow off of his face and tossed it somewhere next to his mattress. Just when he leaned over the side to get up, though, something on it caught his eye.

Picking the pillow back up again, he noticed a red stain on the fabric. He couldn’t recall what it was, or how it got there, but he knew it hadn’t been there before. Could it have been ketchup? No, it smelled far too irony for ketchup.

A metallic-scented red stain on his pillow.

Oh, duh. It was blood. He must’ve had a nosebleed, or something.

With a sigh, he forced himself off the mattress and out of his room, heading to go grab the stool so he could wash his face off in the sink.

He was stopped by a short, shrill scream, and then by the sound of his brother calling his name.

With a quick change of plans, he rushed to his brother’s room, opened the door, and froze.

He had been expecting another nightmare. That, he knew how to deal with.

He never would have thought he’d see Papyrus sitting on the edge of his racecar bed, holding his own skull in his hands instead.

“I C-CAN’T PUT IT BACK ON,” he rasped, his voice far too shaky for this early in the morning. His eyes weren’t focused on anything, but when Sans managed to unstick his slippers from the floor to move closer, he gasped. “WHAT HAPPENED TO  _ YOU?” _

“You’re asking  _ me  _ that question?” Sans asked, struggling to keep his cool when he couldn’t tear his eyes away. “It’s just a nosebleed, don’t, uh, lose your…”

He trailed off, finally averting his gaze to his feet, focusing only on the fluff of his slippers for a few seconds.

_ Drip, drip. _

Blood hit the floor.

Cursing, he angled his head back up to wipe at his nose.

It was… dry?

“YOUR MOUTH, SANS,” Papyrus said slowly. “YOU SHOULD… PROBABLY LOOK INTO A MIRROR.”

Hesitantly, Sans put his hand to his mouth, and it came back red.

When he sucked in a sharp breath, his ribs felt…  _ odd.  _

For the first time that morning, he took a moment to inspect himself.

He didn’t need a mirror to tell him that, somehow, someway, his torso had been sliced in half.

With one final, fleeting thought that he’d  _ finally  _ get some sleep, the world went dark as he passed out.

* * *

He should move.

He was so,  _ so  _ tired, but he couldn’t stay here. He  _ couldn’t. _

He heard rushed footsteps coming towards him.

He had to get up, he had to  _ move-- _

Sitting upright with a loud gasp, Sans heard a voice fade in while he took in his surroundings.

“...ANS, ARE YOU OKAY?” Papyrus all but shouted, nearly dropping his head as he held it with one hand, lightly shaking Sans’s shoulder with the other.

“I, ah, wouldn’t exactly say that,” he replied, rubbing his eyesockets.

“I’M GONNA CALL UNDYNE,” his brother stated, moving to haphazardly rummage through his drawers, probably searching for his cellphone. “OR ALPHYS, OR…  _ SOMEONE,  _ I DON’T KNOW. WHOEVER THE HELL KNOWS WHAT’S GOING ON.”

“Language,” Sans teased, trying his damn best to find  _ some  _ humor in this. He was shot down by a quick, biting glare from Papyrus. With a sigh, he shifted to lean against the wall.

This had already been a long night, but something told him it was about to get a whole lot longer.


	2. The One Where Alphys Needs a Nap

**Summary for the Chapter:**

> The bros find out how Undyne and Alphys are holding up. They could be better, to say the least.

When Undyne opened her door, she was still half asleep.

When she was greeted mid-yawn by the sight of her best friend holding his own head in his hands, she woke up.

“What the _fuck?”_ She shouted, backing up only to slip on some strange reddish goop she hadn’t noticed before. Promptly falling on her ass, she cursed and looked around for the source of the goop. The color of it was almost familiar…?

“LOOKS LIKE YOU DIDN’T GET OFF EASY, EITHER,” Papyrus commented solemnly, shifting his skull to one hand as he extended the other to help her up.

“What are you talking about?” She asked, unable to keep her eyes from darting between his face and the stump of his neck. “Why’s your head _off?”_

“That’s what we’re trying to find out,” Sans answered, peeking out from behind his brother. _His_ appearance wasn’t too reassuring, either.

“You’re bleeding!” Undyne pointed out, confused out of her mind. She refrained from looking lower, where his torso was split in two.

“Yeah,” he agreed with a shrug. “Say, you haven’t looked in a mirror lately, have you?”

Slowly, she crept back into her house, leaving the door open for the two to follow as she slipped back into her bedroom. Standing in front of her mirror, she found she could only stare.

She was _melting._

Her hair seemed to have gotten the worst of it, leaving a red trail behind her as she walked. The rest of her was mostly solid, but certainly not all the way. She could point out more than a few scales that had all but disappeared as they fused with each other.

She braced herself against wall, taking deep breaths.

She wasn’t scared.

She was _angry._

She’d had a dream like this already, but she’d managed to fall back asleep without thinking too hard about it. She had _thought_ it was a dream, anyway.

_(A human rubbing rampant, slaughtering anyone in its path. Papyrus was already dead. There was only one thing she could do, and she’d failed. They only watched as she sank down lower, forcing herself to hold on as long as possible if only to get the others more time, and then-)_

“UNDYNE!” Papyrus said suddenly, giving her arm a gentle touch. “DEEP BREATHS, OKAY?”

She hadn’t noticed she’d started hyperventilating, but as she looked down at the skeleton’s concerned face, she tried to bring herself back under control. 

“D’you think we should go see Alphys?” Sans suggested, scratching the back of his neck. “None of us have a clue why this happened, but she’s got a whole lab where we can try to figure it out.”

Undyne blinked. She _definitely_ had a clue, or at least, she _thought_ she did, but…

Was it really just her?

Maybe it _had_ been just a dream, after all.

“Yeah,” she decided, rushing out of the room and front door of her house without waiting for the brothers to catch up. “Yeah, she’ll know what to do.”

* * *

“A-are you currently in p-pain?” was the first thing Alphys said as the lab’s doors slid open.

“Wha-no??” Undyne answered as the scientist ushered the three of them inside.

“N-Nobody else has been, either,” she remarked, barely giving them a second glance as she flitted around the lab. There were papers covered in chicken scratch strewn about, but she managed to dig some blank paper out of the mess. “Write what happened a-and when you noticed.”

In all the time that Undyne had known Alphys, she didn’t think she’d ever seen her this distracted, if that was even a good word for it. Hesitantly, she grabbed a pen off of Alphys’s desk and began to describe her affliction. After finishing and handing the pen off to Papyrus, she noticed the dark circles under the lizard’s eyes.

“...Hey, uh, Alphys?” She asked, attracting her attention away from the thick stack of papers she was furiously scribbling onto. “How long have you been awake?”

“Since three,” she replied, allowing some exasperation to seep into her voice. “People just k-keep coming and coming a-and I haven’t b-been able to sit down.”

“Why don’t you do that now?” Sans said, nearly putting his own paper down into another pile before Alphys quickly grabbed it out of his hand, adding it to her stack as she shook her head.

“This is a p-problem throughout the entire underground,” she muttered. “P-people are counting on me to f-figure it out as soon as I can.”

“HOW DO YOU DO THAT IF YOU CAN’T EVEN KEEP UP WITH IT?” Papyrus questioned, finally finishing his self-description. Writing was a lot harder when you had to hold your head up to the paper, apparently.

“I’ll f-find that out, too,” she sighed, finally stopping to look at her guests. Her eyes widened a bit. “You three g-got it _bad._ Worse th-than the others I’ve seen, a-anyway.”

“That’s… _not_ reassuring,” Undyne said. There was a bit of comfort in knowing that this happened to others, too, but to know that she got the worst of it soured the effect. 

Alphys’s eyes focused on her for a moment, froze, and quickly looked away. She returned her gaze to the papers strewn about. 

“No, i-it isn’t,” she agreed. 

**Notes for the Chapter:**

> haven't you heard? the royal scientist knows everything about everything that's going on
> 
> (also sorry this one's so short lol)


	3. Make This Make Sense

**Summary for the Chapter:**

> Alphys comes up with a theory, and Papyrus experiments.

Alphys glared at the coffee maker as it stubbornly refused to go any faster.

While she waited, she read through the stack of papers she had collected. She was still getting visits from monsters as the day progressed, but they had died down since the first wave. She had no complaints about  _ that. _

The “injuries,” if you could even call them that, ranged from small scratches and bruises, to Muffet not being able to get a flower out of her hair, to a friend Alphys only knew through Undernet not being able to attach his head to his neck. 

It didn’t make any sense.

She’d had a nightmare before any citizens came to her lab. She had dreamed of hiding while some  _ thing  _ crept around, not even giving Mettaton a chance to speak before she heard the creaking of metal and the sound of an explosion. Then she had dreamed of coming out to see what had happened, and Undyne was on the screen of her monitor, and it was like she was looking straight at her, and she was  _ melting. _

And then Alphys woke up, and Undyne arrived at the lab hours later, still melting.

_ Drip, drip. _

She only knew of one thing that made monsters melt.

_ Drip, drip. _

Undyne couldn’t have gotten that. Alphys never told her about that. 

_ Drip, drip. _

Alphys grabbed the coffee pot, not bothering to grab a mug before she poured in a bit too much creamer. She took a big sip, wrinkling her nose at the heat, and returned her attention to the problems at hand.

She wasn’t going to rest until she figured this out.

First things first: why were  _ those  _ three the ones who were effected the most?

Undyne is the captain of the Royal Guard. She can get hurt easily with a job like that, but she’s usually wearing her armor, and that still doesn’t explain how she would suddenly start melting in the middle of the night.

Sans and Papyrus are both sentries. Not the most dangerous, or even  _ active  _ job, but if a human falls down, they would be the first ones to know. Then they would contact Undyne, and she’d go out to collect the human’s soul.

That was a connection between them. 

But still, why  _ them?  _ Why not the rest of the Royal Guard? They would encounter the human too, no doubt, but they only had a few scratches here and there. 

She sat up suddenly, not remembering grabbing yet another piece of paper to scribble onto, but ignoring it as she came to a realization.

Of course, if a human fell, the Canine Unit would fight them first, but the human wouldn’t be quite strong enough at that point to inflict enough damage to cause serious bodily harm.

They would, however, be  _ more  _ than strong enough by the time they got to Papyrus.

They’d be even stronger by the time they got to Undyne. She would put up one hell of a fight, and she would be…  _ determined  _ to save everyone. Perhaps that would lead to the melting.

And  _ Sans…  _ Well, she wasn’t really sure about that. She knew he had his…  _ thing,  _ in Judgement Hall, but he always gave vague non-answers whenever she asked about it.

She’d have to check in with Asgore and Mettaton soon, to see if they were injured as well. If they were, it would certainly help add to her theory.

There was one huge problem, though.

A human hadn’t fallen into the underground in  _ years.  _ The last time one had fell, she was still wearing stripes. She was sure she’d remember if one started killing everyone last night, and considering everyone was still alive and unhurt, she began to doubt herself.

But she also knew that humans were very determined creatures, even more so than Undyne.

And determination had always been a very,  _ very  _ powerful thing.

She had more research to do.

* * *

Papyrus stomped through the snow, holding his head up in the air to at least  _ feel  _ like he didn’t get his height chopped down a few too many inches.

After a few minutes of pacing, he stopped in his tracks and fit his skull back where it should have been the whole time.

He held it there for a minute, gritting his teeth in discomfort as he pressed down.

Then he let go, cursed as he failed to catch it, and watched the world spin until it landed next to his foot.

He rolled his eyes for what felt like the hundredth time that day, realizing he wasn’t facing his body. After an awkward moment of feeling around blindly, he picked his skull back up and returned home.

“CROSS  _ ‘SNOW’  _ OFF THE LIST,” he huffed, wiping his boots off on the doormat.

“Did you really think that would work any better than ice?” Sans asked from where he was laying on the couch, crossing something off in the small notepad he was holding.

“DID  _ YOU  _ REALLY THINK RAMEN NOODLES WOULD WORK ANY BETTER THAN GLUE?” Papyrus snarked back, nudging his brother’s slippers away before taking a seat himself.

“Hey, you  _ saw  _ those videos--”

Sans’s defense of himself was cut off by a knock at the door, though it sounded more like a few rocks were being thrown at it instead of a person’s knuckles.

Standing up again, Papyrus balanced his head in one hand and opened the door with the other.

Outside was a small, yellow flower, though the color had faded from his ripped petals. He stared up at the skeleton with an unreadable expression, his face nearly familiar in all the wrong ways.

“Papyrus,” he said. “I have something I need to tell you, and I need you not to freak out.”


	4. Realizations

**Summary for the Chapter:**

> Two monsters come to some conclusions that are far less than ideal.

“I’LL BE BACK IN A BIT, SANS,” Papyrus announced, not looking back as he stepped outside and closed the door behind him. He wiped some snow off of the steps and sat down, resting his skull in his lap.

“I’ll just cut to the chase,” Flowey said curtly. “A human is going to fall down a few days from now.”

“OH!! FINALLY, WE-”

“They’re going to kill everyone.”

“...OH.”

“Yeah. Hold off on the crushing disappointment for now.”

“IS THAT WHY… DID THEY-”

“Yes, they already did. Something weird must have happened to make everyone be effected like this, and I don’t know  _ what,  _ but they’re definitely gonna go for a repeat.”

Papyrus took a deep breath, lightly tapping a finger against his cheekbone. 

“WHAT DO WE DO, THEN?” He asked. Flowey looked away, and with his strange new face, he almost looked guilty.

“Well, I have a plan, but you aren’t gonna like it,” he stated. “Papyrus, you know you’re pretty much the only line of defense between Snowdin and Waterfall, right?”

“WHAT ABOUT THE DOGS?”

_ “Please,  _ they’re more incompetent than your brother.” Papyrus opened his mouth to protest, but Flowey kept going before he could say anything. “No,  _ you  _ are the only person capable of giving the human a real challenge before they get to the rest of the underground.”

“...I DON’T THINK I LIKE WHERE YOU’RE GOING WITH THIS.”

“I told you so,” Flowey snickered. Then his stem rose further from the ground, and he leaned in close to Papyrus’s face. “Listen, I know you’re gonna want to spare them, but you  _ already did that,  _ and  _ look  _ where it landed you. The last time you trusted them, they killed  _ everyone.” _

Papyrus stared at the ground. He felt nauseous.

“If you want to save the underground,” Flowey said, “you can’t let that thing live."

* * *

“T-tell me if this sounds crazy, okay?” Alphys stammered, avoiding eye contact by looking at everything in the room that wasn’t the fish monster in front of her.

“Okay?” Undyne agreed, more confused than anything.

“So, a human falls down into the underground,” she made big motions with her hands, like it helped her make sense of what she was saying, “a-a-and they decide that they h-hate all monsters, that they want us d-dead, right?”

Undyne squinted, prompting her to go on.

“W-well, since they hate us and want us d-dead, they do just that! And they kill us!” Alphys exclaimed. “Which they can do because they’re a human and they have a lot of determination, wh-which is extremely powerful and terrifying when you have a lot of it but that’s not the point-- s-so, they kill us all and then suddenly, um. Regret it? D-do I sound crazy yet?”

“...You’re getting there,” Undyne said.

“I-I figured. So anyway, they regret killing us all f-for some reason, so they find s-some way to reverse it all. To rewind time i-itself back to before they killed us, b-but something-- I don’t know what-- messed up, and the underground wasn’t reverted to its original state,” she took a breath, pushing her glasses up with shaky hands, and Undyne wondered how much coffee she’d had today. “Which leads to most of us suddenly being stuck in a half-dead, half-living state overnight. Wh-what do you think?”

She finally looked at Undyne, her expression hopeful, yet horribly nervous.

But Undyne didn’t say anything.

Instead, she thought about her nightmare, how it had felt so  _ real  _ and how maybe-- just  _ maybe--  _ it could have been more than just a dream.

“Do you want to hear something more crazy?” She asked finally as Alphys looked more nervous by the second.

“Wh-what?”

“I believe you,” she answered, “because I think I can remember that happening.”

Alphys froze for a second, then gasped, her eyes watching some scales drip off of Undyne’s arm.

_ “You have determination!”  _ She all but yelled, jumping up from her chair hard enough for her tail to throw it back. “Of course you’d remember it! That explains th-the melting, too! I-I can’t believe I didn’t realize…”

She trailed off, staring at nothing. Then she looked back at Undyne, her eyes wide.

  
“I-if I  _ am  _ right, then…” She said. “That human’s gonna come back.”

**Notes for the Chapter:**

> Sorry this one was super short & also took me so long to get out!! I took a break from this to work on another thing and the break ended up lasting for like 30 years

**Author's Note:**

> local dumbass doesn't notice he's been cut in half and bleeding from the mouth for several hours


End file.
